Pt/Ga₂O₃-Al₂O₃ Catalyzes CO₂ Oxidation Propane Dehydrogenation

Propylene is an important basic chemical raw material,and is widely used in large demand.For a long time,propylene was mainly derived from naphtha cracking and catalytic cracking.These traditional processes have not only low propylene selectivity,but also high energy consumption.Propane dehydrogenation to propylene technology has attracted much attention because of its high olefin yield,and has been applied in industrial production.However,the current dehydrogenation technology has the following two deficiencies.One is that the conversion of propane is difficult to be further improved due to the thermodynamic equilibrium limitation,and the other is that the catalyst is rapidly deactivated at high temperatures and thus requires frequent regeneration.Propane oxidative dehydrogenation has attracted much attention because it can reduce the reaction temperature while eliminating the coke on the surface of catalyst.In recent years,the oxidative dehydrogenation of propane has used CO2 as a weak oxidant.This exploration has overcome the problem of prone to overoxidation in the oxidative dehydrogenation with oxygen as the oxidant and the resulted low selectivity of propylene.At the same time,the effective use of CO2 is of great significance to not only CO2 reduction and reduction,but also the realization of China's carbon neutrality goal.The catalyst is the key to the propane dehydrogenation technology.It is very important to develop a catalyst with excellent performance.Pt-based catalysts can effectively activate the C-H bonds of alkanes.The choice of support has a huge impact on the catalytic activity of Pt-based catalysts.Traditional Pt-based catalysts usually use?-Al2O3 as the carrier.The strong interaction between metal and ?-Al2O3 is conducive to the dispersion of Pt onto ?-Al2O3.However,the strong acidity of ?-Al2O3 may cause a large amount of carbon deposits on the surface of the catalyst and the resulted rapid deactivation of the catalyst.Ga2O3-Al2O3 solid solution has high specific surface area,more weak acid sites and thermal stability,and thus is expected to be a promissing carrier for the catalyst of dehydrogenation of propane.In addition,the introduction of Sn as a promoter in Pt-based catalysts can inhibit sintering and coking to a certain extent,thereby slow down the deactivation of the catalysts.In this thesis,Ga2O3-Al2O3 solid solution was intentionally synthesized as the carrier,and a series of supported Pt/GaxAl10-xO15(x=0,2,5,8,10)catalysts and Sn-doped PtySn/Ga8Al2O15(y=0,1,3,5)catalysts were prepared.XRD,H2-TPR,TEM,NH3-TPD methods were employed to characterize the structure and performances of the catalysts.A fixed-bed reactor system was used to evaluate the performances of the catalysts in the dehydrogenation of propane under CO2 atmosphere so as to develop a promising catalyst for the CO2 oxidative dehydrogenation of propane(CO2-ODHP).The main contents and results are as follows:(1)Catalytic CO2-ODHP over Pt/Ga2O3-Al2O3A series of GaxAl1O-xO15(x=0,2,5,8,10)solid solutions with different Ga/Al molar ratio were prepared by solvothermal method,on which a series of supported Pt/GaxAl10-xO15(x=0,2,5,8,10)catalysts were prepared by incipient wetness impregnation method.It was found that Pt is well dispersed on the Ga2O3-Al2O3 carrier.Pt/GaxAl10-xO15 had larger specific surface area and more weak acid sites.With the increase of Ga content,the weak acid sites on the surface of the catalyst increased initially and then decreased,so did the catalytic activity.The catalytic activity of Pt/Ga8Al2O15 is the best when the Ga/Al molar ratio is 4/1(the initial conversion of propane is 36.6%,and the selectivity of propylene is 85.4%).In addition,the Pt/Ga8Al2O15 catalyst has better activity and stability at 500?.The main reason for the deactivation of Pt/Ga8Al2O15 may be carbon deposition.While fortunately,CO2 may eliminate the amorphous carbon on the surface of the catalyst to a certain extent,and thus slow down the deactivation of the catalyst.(2)Catalytic CO2-ODHP over Sn-doped Pt/Ga2O3-Al2O3A series of Sn-doped PtySn/Ga8Al2O15(y=0,1,3,5)catalysts with different Sn/Pt molar ratios were prepared by incipient wetness impregnation method.The structural properties of the catalyst were characterized by several techniques,such as H2-TPR and C3H6-TPD.The catalytic performance of CO2 ODHP was evaluated,and the impacts of promoter Sn on the catalytic performances were investigated.It was found that with the increase of Sn content,the catalytic activity increases initially and then decreases.When the Sn/Pt ratio is 3/1,the catalyst has the best catalytic performance(the initial conversion of propane is 48.2%,and the selectivity of propylene is 96.3%).As compared with the results obtained in the catalytic CO2-ODHP via Pt/Ga2O3-Al2O3,it is clear that doping with Sn can effectively improve the activity and selectivity of the catalyst.Based on the C3H6-TPD results,it is believed that the presence of Sn species on surface of the catalyst may effectively promote the desorption of C3H6.